One of the desired performance objectives of disposable, personal care absorbent products is to provide an article that provides proper fit for the wearer, while maximizing containment with minimal leakage. It has been found that the ideal shape for absorbent components of articles such as disposable diapers, adult incontinent articles, and training pants are those which tend to be narrower in the crotch region, than in the front waist region, and rear region under the buttocks. By use of absorbent components shaped in this fashion, the desired fit and containment characteristics are maximized, while leakage is minimized. Similarly, sanitary napkins have also been found to be more comfortable when they are generally hourglass-shaped or dumbbell-shaped, with a narrower center portion, and relatively wide end portions.
In the case of disposable baby diapers and training pants, there are conflicting considerations between problems of urine leakage, and the width of the absorbent component in the crotch region of the article. For example, on a toddler, the minimum diaper absorbent core width in the crotch that allows the best fit is on the order of about 60 millimeters, depending on the specific design of the product. It has also been found that as the diaper absorbent core crotch region is made less than 95 millimeter in width, urine leakage tends to be a significant problem. There are several reasons for this. By making the core crotch very narrow, the amount of absorbent material in this region that is available to manage fluid surges becomes inadequate. There is insufficient void volume, and insufficient surface area, in order to pass the liquid into the core, and manage it in this area of heavy loading. Another mechanism by which the crotch shape of absorbent core affects leakage performance is its ability to seal against the leg of the wearer in the crotch area and in the region forwardly thereof, preventing liquid from getting off of the core surface. The body position of the wearer is highly variable, and finding the shape that gives the most consistent seal requires special consideration.
As the absorbent core of an article in the crotch region is widened, the core is required to bunch-up into a pleated shape or condition in order to fit the crotch region between the legs of the wearer when the legs are closer together than the width of the diaper crotch area. In addition to being uncomfortable, this geometrically tends to pull the diaper downwardly. Other conflicting considerations arising from use of a widened core in the crotch region is that ideally, functionally elasticized leg flaps are typically desirably placed a minimal distance from the core, such as contemplated by U.S. Pat. No. 3,860,003, to Buell. If the crotch region of the core is made wider, these leg elastics are then required to be more widely placed, which in turn causes it to be necessary to make the crotch width in the envelope or “surrounds” of the diaper wider as well, since these components must be positioned outwardly of the leg elastics. This wide envelope crotch portion, when bunched-up between the legs of the wearer, causes wrinkles that tend to gather the waist of the diaper inwardly.
The net consequence of a diaper absorbent core crotch portion being wider than ideal is threefold. The crotch of the article is perceived as bulky and uncomfortable, the diaper cannot be pulled up as far so it seems to be shorter in length, and the waist material is bunched toward the centerline of the article, so that the waist size is perceived as being smaller.
Those skilled in the art are aware of the compromise between fit and leakage performance. Because consumers tend to place a higher value on leakage performance than they do on fit, there is a tendency to have crotch regions of absorbent articles be relatively wide, much wider than the ideal. For example, most size “large” disposable baby diapers sold in the United States markets have absorbent core crotch portions between 90 millimeters and 100 millimeters wide. This is much wider than the ideal 60-70 millimeter width that would yield the best fit. In the context of the present invention, this means that it is necessary to have the ability to design an absorbent core crotch portion to the shape which is known to provide the best value.
In the front waist region of disposable diapers (and to a lesser degree in disposable training pants), it has been found to be advantageous to have a wider core, in order to minimize leakage. There are several reasons for this. It has been found to be advantageous to have the sides of the absorbent core in contact with the wearer's legs in order to quickly absorb any liquid in that region, rather than risking allowing liquid to pool there behind the leg flaps. In order to follow the shape of the front of the thighs far enough forward to be effective, an absorbent core should contact the curves of the thighs toward the front, until the core is much wider. For example, a size “large” baby diaper would ideally need to follow the thighs until it is at least 110 millimeters wide to take advantage of this sealing effect. Many designs are much wider than this.
A second reason for broadening or widening of the absorbent core in the front of the diaper is to provide sufficient surface area in order to manage fluid surges. There has been a great deal of technology developed to manage urine surges. For example, U.S. Pat. No. 5,490,846, to Ellis, discloses the application of low density nonwoven fabric structures intended to provide sufficient void volume in the core to rapidly acquire surges. U.S. Pat. No. 5,294,478, to Wanek, teaches the application of a two-layered acquisition structure, with a lower layer that is more hydrophillic and with a smaller average core size than the upper layer. However, a problem with these materials is that they are still inadequate in some situations to absorb urine sufficiently rapidly, and as a result, liquid flows downwardly on the surface of the diaper core. If the baby is laying on its side, it is a very short distance before the liquid runs off of the core. U.S. Pat. No. 4,695,278, to Lawson, contemplates the use of upstanding barrier cuffs which run laterally along the sides of the core, and are intended to stop any of this liquid runoff, and redirect it back into the core. In the front region of a diaper, the cuffs are flat against the body, and the resulting channel formed behind them and the associated barrier effect, are very unreliable. Liquid reaching the sides of the core in the front region of the diaper is likely to run off the core, and out the leg. Those skilled in the art know that a baby laying on its side, particularly a boy, presents one of the most challenging positions in terms of leakage containment. By making the absorbent core wider in the front of the diaper, and at a minimum, filling the entire region between the barrier cuffs with core material, it is possible to increase the distance that the liquid can run downwardly toward the side of the diaper, before it reaches the edge of the core. Leakage is thus reduced. Ideally, this requires an absorbent core wider in the front waist region than in the crotch region.
A third advantage to having a wider core in the front of the diaper is that it is a relatively short distance for liquid to travel out the front waist region. Many designs employ elasticized waistbands and elasticized barrier flaps along the waistband of the diaper, intended to stop run-off from leaking out the waist when the wearer is in the front position. These features have not proven to be reliable, and a wider absorbent core in the front waist region provides more absorbent material to absorb this flow.
Another advantage to having a somewhat broader absorbent core in the front region of a diaper is that the core material causes the tape landing zone (TLZ) for the closure tapes to be held in a flat, smooth condition. This makes the fastening system somewhat easier to operate. If the absorbent core is narrower than the landing zone, then a “step” in the height of the landing zone is observed at the outer edges thereof, making fasteners secured at these areas less secure.
In the case of disposable diapers, it has been found by those skilled in the art that it can be advantageous for the absorbent core to be somewhat wider in the back of the diaper, under the buttocks, as well as wider in the front. This is reflected in a majority of typical United States domestic diaper designs. Bowel movements in infants are frequently very liquid, and leakage is a significant problem. Those skilled in the art know that the back portion of the absorbent core absorbs the liquid from the BM, increasing the viscosity, and rendering it much less mobile. Any BM that contacts the core is dewatered in this manner. Any BM that falls to the sides of the core is not dewatered, and has a much greater chance of leaking out the leg. Those skilled in the art know that by making the absorbent core in the back somewhat wider, until it fills the zone between the barrier cuffs, results in BM leakage that is frequently reduced, depending on the diaper design.
In sanitary napkin applications, the design goal is for the fit to allow the napkin to conform to the body, automatically position itself on the wearer, provide an acceptable level of comfort, and provide discrete appearance. U.S. Pat. No. 3,805,790, to Kaczmarzyk, teaches that after doing anatomical studies, it was found that there was less variation in the perineal region than was originally thought. This patent teaches that the ideal narrowest width for the sanitary napkin is between 1.25 and 1.75 inches. The lateral sides of the sanitary napkin should have a radius to fit against the legs greater than 2 inches and less than 4 inches. The arch length should be between 1.25 and 5 inches along these lateral edges. In a manner similar to diaper design, there exists a trade-off between the width at the narrowest point of the napkin, and the incidence of leakage and soiling. As a consequence of these design requirements, most sanitary napkin designs in the United States have an absorbent core shape which tends to be dog bone shaped, or hourglass-shaped, and rounded on the ends. Again, the requirement is for a non-rectangular core for sanitary napkin applications.
Absorbent articles using preformed absorbent cores are known in the prior art. As will be further discussed hereinafter, the present invention relates to formation of shaped components, such as absorbent cores, for disposable absorbent articles, which are first formed on a wide-web machine, longitudinally slit into two or more individual subdivided webs, and then delivered to a converting machine, in some appropriate package, in order to be converted into the finished absorbent articles. The alternative to this formation technique is to form an absorbent core on the converting machine itself. Some examples of technologies for producing these preformed absorbent cores include air-laid, wet-laid, and carded webs. These cores may incorporate cellulosic fibers, such as wood pulp fibers or cotton linters, superabsorbent polymeric materials, and synthetic staple fibers. These cores may also incorporate cross-linked cellulosic fibers, or cellulosic fibers which have been otherwise modified chemically to enhance their properties.
There are several reasons why it is advantageous to use a preformed absorbent core structure made on a wide web machine, rather than making the core structure on the converting line. First, the degree of complexity of the converting line is desirably reduced. By moving processes such as core formation off-line, the possibility of the line going down is reduced. This is particularly advantageous in connection with manufacture of more complex product designs, where many unit operations are involved. Secondly, wide web technologies have generally proven to reduce variation in basis weights, relative to traditional core formation systems done on converting machines themselves. This reduction in basis weight variation, combined with the simplification of the converting line, ultimately facilitates operation at higher line speeds.
Another advantage of off-line manufacture is that as absorbent cores become thinner, it is necessary to introduce additional core manufacturing technologies, such as thermal bonding, resin bonding, incorporation of staple fibers, and the like, in order to optimize the performance of the absorbent cores. These technologies are more readily implemented on a wide web machine that runs continuously, rather than on individual converting machines that typically start up and shut down relatively frequently. From the consumer standpoint, the preformed absorbent cores tend to be much thinner than the conventional cores, providing the potential for significantly enhanced fit.
One problem with current practice for making preformed cores on a wide web machine is that the web is slit in straight lines, and the resultant absorbent cores are rectangular in shape. The designer of the absorbent article is then required to cut the core to the desired shape, resulting in material waste, or must compromise between narrow dimensions in the center region, and wider dimensions in the end regions of the core. In applications requiring absorption of urine, the consumer places a high value on leakage performance, and leakage performance is enhanced by having a wider core. Consequently, the core widths frequently are chosen wider than diaper designs made with conventional cores. The crotch regions are therefore typically bulky, which negates much of the perceived value of having a much thinner, preformed core. Alternatively, the converter can die-cut the preformed core material into a more fitted shape, but this can result in significant material waste.
There have been a significant number of developments in the prior art aimed at producing a fitted shape from a rectangular core, while minimizing or eliminating material waste. European Patent No. 670153 teaches cutting a rectangular web into a substantially hourglass shape, while leaving the cut-outs attached at the root of the crotch portion. The cut-outs are folded over on top of the web, resulting in higher base weight in the crotch, as well as a no-waste application. While the additional basis weight in the crotch area is sometimes desirable, the shape of this double layer region is frequently complex, and results in thicker edge portions in the crotch region. The resulting center region can then take on a lumpy appearance.
PCT Patent No. WO/9829070 teaches that a pair of webs, which are shaped and include protruding structures, are partially nested in order to reduce the waste. While saving some waste, there is still some waste present in this arrangement, and there is thus a conflict between the degree of nesting that can be achieved, and the quantity of waste that results.
U.S. Pat. Nos. 5,695,846 and 5,597,437 teach the practice of cutting a fully shaped absorbent core from a continuous web, and then superimposing the removed strips onto the core. The removed strips are attached in a manner such that the complementary shapes on the strips coincide with the shape of the fully shaped core to which they are laminated. In order to do this, the design options for the core are severely limited to shapes where the complementary strips of material removed from the sides of the web can superimpose perfectly on the shaped core from the center of the web.
U.S. Pat. No. 6,171,432 teaches the practice of slitting a rectangular web into two webs, with a single shaped cut forming two strips each with one straight side and one shaped side. They are repositioned, phased, and joined to one another along the straight side, forming a longitudinally symmetrical web with shaped sides. This method also severely limits the types of shapes which can be used, as the complementary shapes produced by the slit must be identical when re-phased and joined together in order to produce a longitudinally symmetrical core.